When the Doctor and Jo accompanied Spiridakis and Katsoudas to their dig site, Spiridakis and Jo took the lift underground. Katsoudas started an earthquake, trapping Jo and injuring Spiridakis.
Spiridakis was being hypnotised by Katsoudas, but fought it to help rescue Jo from the Master and stop his plans. However, the Master's device aged Spiridakis to death before the Doctor could get him to the TARDIS. (PROSE: The Seismologist's Story)